The mechanisms of pathogenesis of equine infectious anemia virus (EIAV) is being investigated. The role of related viruses in other diseases is also being assessed. To pursue these problems, EIAV proteins are being produced by using prokaryotic expression systems. The EIAV gag gene precursor has been expressed in E. coli and milligram quantities have been obtained which have made possible development of sensitive radioimmunoassays for EIAV.